The present disclosure relates to a fusing system including a heat distribution mechanism. More particularly, the disclosure relates to a fusing system including a heat pipe that can be used to distribute heat across the fusing system.
Electrophotographic printing and copying devices typically are provided with fusing systems that serve to thermally fuse a toner image onto a recording medium, such as a sheet of paper. Such fusing systems normally comprise a heated fuser roller and a heated pressure roller that presses against the fuser roller to form a nip in which the fusing occurs. The fuser and pressure rollers typically comprise hollow tubes that surround internal heating elements and are coated with outer layers of elastomeric material.
The internal heating elements typically comprise heating lamps and/or nichrome heating elements that uniformly irradiate the inner surfaces of the rollers. Through this irradiation, the inner surfaces are heated and this heat diffuses to the outer surfaces of the fuser and pressure rollers until they reach a temperature sufficient to melt the toner (e.g., approximately between 160xc2x0 C. to 190xc2x0 C.). The fuser roller and the pressure rollers rotate in opposite directions and are urged together so as to form a nip that compresses the outer layers of the rollers together. The compression of these layers increases the width of the nip, which increases the time that the recording medium resides in the nip. The longer the dwell time in the nip, the larger the total energy that the toner and recording medium can absorb to melt the toner. Within the nip, the toner is melted and fused to the medium by the pressure exerted on it by the two rollers. After the toner has been fused, the recording medium is typically forwarded to a discharge roller that conveys the medium to a discharge tray.
During use of the device, thermal loads are applied to the fusing system from contact with the recording media during fusing. The temperature of the roller outer surfaces drops at regions in which contact is made with the recording media. If the thermal load is not uniform across the surface of the rollers (i.e., if the media is more narrow than the length of the rollers) a non-uniform temperature distribution (i.e., temperature gradient) results. For example, when relatively narrow media (e.g., envelopes, postcards, etc.) are passed through the fusing system, the temperatures on the outer surfaces of the rollers will be much lower where contact is made with the media as compared to areas in which such contact is not made.
Typically, the temperature of these surfaces is controlled using negative feedback. For instance, when a thermal load is applied to the fuser and pressure rollers, the power supplied to the rollers is increased to maintain the operating temperature of the rollers. In that the outer layers of the rollers are normally constructed of rubber materials (e.g., silicon rubber) that have high thermal resistance, and since the rollers are normally internally heated, the return to operating temperature is delayed by the outer layers. Because heating of the rollers is not limited to the areas at which a thermal load is applied, such heating can raise the temperatures of the unloaded regions of the outer layers, typically adjacent the ends of the rollers, to the point at which degradation (e.g., delamination) of the layers can occur. Notably, such damage can also occur even where internal heating is not used in that destructive temperature gradients can be created across the length of the fusing system rollers any time the width of the recording media is smaller than the length of the rollers.
From the foregoing, it can be appreciated that it would be desirable to have a fusing system in which thermal gradients that arise during use can be quickly reduced such that a substantially even heat distribution is maintained across the fusing system rollers.
The present disclosure relates to a fusing system for fusing toner to a recording medium. In one embodiment, the fusing system comprises a fuser roller configured as a heat pipe including an inner tube and a coaxial outer tube that is mounted to the inner tube, the inner and outer tubes defining an interior space therebetween that is adapted to contain a liquid and to be evacuated so as be maintained in a vacuum, and a pressure roller in contact with the fuser roller. In another embodiment, the fusing system comprises a fuser roller, a pressure roller in contact with the fuser roller, and an external heating roller in contact with the fuser roller, the external heating roller being configured as a heat pipe including an inner tube and a coaxial outer tube that is mounted to the inner tube, the inner and outer tubes defining an interior space therebetween that is adapted to contain a liquid and to be evacuated so as be maintained in a vacuum.
The present disclosure also relates to a method for distributing heat within a fusing system. In one embodiment, the method comprises the steps of providing a fuser roller including an interior space maintained in a vacuum that contains a liquid, heating the fuser roller until the liquid within the interior space is vaporized, and distributing heat within the fuser roller via continual condensation and re-vaporization of the vaporized liquid within the interior space. In another embodiment, the method comprises the steps of providing an external heating roller including an interior space maintained in a vacuum that contains a liquid, placing the external heating roller in rolling contact with a fuser roller of the fusing system, heating the external heating roller until the liquid within the interior space is vaporized, and distributing heat within the external heating roller via continual condensation and re-vaporization of the vaporized liquid within the interior space.
The features and advantages of the invention will become apparent upon reading the following specification, when taken in conjunction with the accompanying drawings.